Another thought - Misch metal is very sensitive to moisture. Could the water collected by the black powder fouling be an issue here?
---from the web---
Praseodymium, which is named from the Greek prasios + didymos (green twin), was isolated and identified by von Welsbach in 1885 from what was known at the time as didymium. von Welsbach's work revealed that this "substance" actually contained two new elements, one of which was praseodymium (neodymium was the other).
Pure praseodymium is silvery-white and fairly soft. It oxidizes slowly in air and reacts vigorously with water to release hydrogen gas. It is used as an alloying agent along with magnesium for parts in aircraft engines. Misch metal is 5% praseodymium and is used for alloying steel and in flints used to create sparks in lighters. The glass in welder's goggles contains a mixture of praseodymium and neodymium.
Discovered in 1885 along with praseodymium, neodymium is named from the Greek neos + didymos (new twin). The silvery-white metal oxidizes easily in air and reacts with water, displacing hydrogen gas. Although another of the "rare" earth metals, neodymium is actually more abundant than many better known metals such as gold, silver, tin and lead.
Misch metal, used in lighter flints, is about 18% neodymium. The element is also used in the manufacture of artificial rubies for laser applications.
That makes what pyrite I do have even more precious.
